HEREDITY AND MUTATION AS CELL PHENOMENA 525 
gradual drawing apart from its parent, except in so far as different 
organs may be unfolded in the later development. Already in the 
fertilized egg the difference is present, and makes itself felt as much 
in the first leaves as in the last. It is therefore important to remember 
that a mutant is such because not only its germ cells but every one of 
its somatic cells contains a certain peculiarity. 
This is probably as true of animals as it is of plants, though an 
important difference is introduced here by the fact that in animals 
the germ cells are very early set apart from the somatic cells, while 
in higher plants this only happens with actual flower production. 
If we compare the dimorphic condition of the cells in the males 
and females of certain insects with the difference between the cells of 
Oe. lata and Lamarckiana, it is clear that these differences correspond 
in certain features. The females of Anasa tristis have two members 
of a certain pair of chromosomes where the males have only one. 
Though the germ cells are set apart very early in the ontogeny in 
insects, yet it is probable that these chromosome differences occur 
not only in the young embryos, where they have been actually ob- 
served, but throughout the somatic tissues. A female animal, like a 
mutant, is somatically distinguished by having a different chromosome 
content in all its tissues, and not merely by the possession of female 
sex glands or secondary sexual characters. So far as I am aw^are, the 
fundamental significance of these facts in their bearing on heredity, 
embryology and variation, to say nothing of the structure of the cell, 
has not hitherto received attention, except in the case of cell giants. 
The fact that mutants differ from the parent in their every cell carries 
with it many important implications. 
Giant mutations are now known in various organisms in the absence 
of tetraploidy. In such cases, although the cells are gigantic the 
chromosome number is unchanged. There is at present no clear indi- 
cation of the fundamental nature of this type of cell gigantism. One 
of the best known instances is that of the giant variety White Queen 
Star, of Primula sinensis, described by Keeble."^ This appeared in the 
normal' variety and breeds true, but crossing experiments indicate 
that it may result from the presence of three independent factors. 
Various tetraploid giants of Primula have also been obtained. 
No doubt there are many other types of chromosome change 
^ Keeble, F. 1912. Gigantism in Primula sinensis. Journ. Genetics 2: 163- 
188, pi. II. 
